This invention relates to x-ray imaging or x-raying using contrast agent, and more particularly to an imaging system which can preferably adopt an energy subtraction technique for imaging.
One example of the devices of obtaining a subtraction image between two images taken at different x-ray energy spectra is disclosed in U.S. Pat. No. 4,445,226 to William R. Brody. This prior art discloses the following two imaging techniques. (1) X-rays with different energy spectra are provided through the filtration of a broad-energy bandwidth x-ray emitted from an x-ray tube using two different filters. By rapidly exchanging these filters, images with different energy spectra are sequentially taken. (2). A broad-energy bandwidth x-ray emitted from the x-ray tube is used as x-ray source. The x-ray images are simultaneously taken using an energy-sensitive detector. Some data processing between the images with different energy spectra obtained in the manner of (1) or (2) provides an objective subtraction image.
The configuration in the manner of (2) is advantageous in that it provides an accurate subtraction image even if an object is moving. The energy-sensitive detector disclosed in the above reference consists of an array of two kinds of scintillators stacked at the front and back part thereof; the scintillators in the front part detect the lower energy x-rays while the scintillators in the back part detect the higher energy x-rays which have passed the front part of the detector. Such a configuration, however, cannot provide a sufficient resolution of energy spectra. More specifically, as proposed in U.S. Pat. No. 4,432,370 to E. Barrie Hughes et al, if iodine is introduced as a contrast agent into a body to be examined (e.g. vein), and two imagings are carried out using monochromatic x-rays at the energies slightly above and below the K-absorption edge of iodine so as to obtain a subtraction image, unnecessary tissue images are cancelled out to provide a clear contrast of the image. In order to successfully achieve this, however, a detector having such a resolution as permitting very adjacent two spectra to be separated and detected is required. It was difficult to obtain a satisfactory result by using the energy-sensitive detector disclosed in U.S. Pat. No. 4,445,226 in the method of U.S. Pat. No. 4,432,370.